In recent years, optoelectronic devices, such as photovoltaic cells, light emitting diodes, and laser diodes, have generated a great deal of interest as an alternative source of energy, an illuminating element for display, or as a display element itself. The emissive characteristics of light emitting devices, for example, are known to be based on the mechanism of recombination, by which electrical energy is converted into photon energy. It is the recombination efficiency in the active (or quantum well) layer of the light emitting device that determines the internal quantum efficiency of the device.
Recent studies are being focused on light emitting devices having a nitride semiconductor such as indium gallium nitride (InGaN) in the active layer, which is found to exhibit full solar spectrum capability. In addition, Group III-V nitride based radiation resistant photovoltaic cells are being examined. However, the nitride material in the active layer tends to cause strong piezo effects on the electric field due to the difference in lattice constants between the active layer and the cladding (or barrier) layers. The piezo electric field, in turn, causes the wave functions of the electrons and holes in the active layer to separate from each other and decrease the recombination rate of the electrons and holes drastically, thereby degrading the adsorption coefficient and the efficiency of the device.